The present invention relates to a solid electrolytic capacitor and, more particularly, relates to a capacitor having a small equivalent series inductance for reducing impedance at high frequencies, which is used on the secondary side of a power supply smoothing circuit and on the periphery of a CPU of a computer, and to a capacitor built-in board using the same.
Recently, with the digitization of electronic equipment, capacitors used for the electronic equipment have been strongly demanded to have larger capacitance and lower impedance at high frequencies. To meet this demand, solid electrolytic capacitors are suitable in terms of large capacitance, and attempts have been made to reduce equivalent series resistance (hereinafter abbreviated as xe2x80x9cESRxe2x80x9d) and reduce equivalent series inductance (hereinafter abbreviated as xe2x80x9cESLxe2x80x9d) resulting from the external terminals of the capacitors.
As these solid electrolytic capacitors, JP 4(1992)-123416 A discloses a small-sized and large-capacity solid electrolytic capacitor that employs a dielectric layer obtained by applying anodic oxidation to a surface of aluminum foil, JP 4(1992)-48616 A discloses a small-sized and large-capacity solid electrolytic capacitor in which a dielectric layer, an electrolyte layer and, a conductive layer are generated successively on both surfaces of a sheet-form anode body and a cathode terminal is provided thereon, and JP 6(1994)-267802 A discloses an electrolytic capacitor in which an anode is formed on one surface of a dielectric layer and a cathode is formed on the other surface and two terminals are provided for each of the cathode and the anode, where a pair of one of the two cathode terminals and anode terminals is assigned as input terminals and a pair of the remaining cathode terminal and anode terminal is assigned as output terminals.
Referring to FIGS. 16A and B, a conventional solid electrolytic capacitor used at high frequencies will be described below. FIG. 16A is a perspective view of the conventional capacitor and FIG. 16B is a cross-sectional view of the same capacitor. As shown in FIG. 16A, an anode terminal 32 and a cathode terminal 33 respectively are led out from two opposed surfaces of a package 31. A capacitor element basically is typified by a dielectric layer 34 sandwiched between the anode terminal 32 and the cathode terminal 33 as shown in FIG. 16B, and solid electrolytic capacitors are used for the purpose of small size and large capacity.
In general, such solid electrolytic capacitors are manufactured as follows: an anode oxidation coating is formed on an etched valve metal thin plate to form dielectrics, and a solid electrolyte layer, a carbon layer and a silver conductive resin layer are formed in this stated order on this dielectrics at a portion expect for an anode leading-out portion. Then, the anode terminal 32 and the cathode terminal 33 are connected to this capacitor element, followed by transfer molding, potting and the like so as to form the package 31.
However, the above-described conventional capacitor is disadvantageous in that a distance between the anode terminal and the cathode terminal is increased, thus increasing ESL and impedance at high frequencies.
In addition, in a capacitor built-in board with the conventional capacitor disposed in the board, currents to flow through a land portion of a printed wiring become more likely affected by the skin effect in accordance with increases in frequency, which hinders the currents from flowing effectively inside the capacitor element. As a result, this capacitor built-in board has a drawback of being incapable of making full use of the capacitance of the capacitor and minimizing its inductance.
It is an object of the present invention to provide a capacitor with low ESL, and moreover to provide a capacitor built-in board with high-performance at high frequencies.
To achieve this object, a capacitor of the present invention includes: a capacitor element including a dielectric layer, and an anode and a cathode that are arranged to support the dielectric layer therebetween; a planar anode terminal formed by prolonging the anode or connected with the anode; and a planar cathode terminal formed by prolonging the cathode or connected with the cathode. The anode terminal and the cathode terminal are led out from the capacitor element in a same direction so as to be in parallel with each other, and at least a part of the anode terminal and at least a part of the cathode terminal overlap each other without contact in a direction perpendicular to a terminal plane of at least one terminal selected from the anode terminal and the cathode terminal.
With this configuration, a distance between the anode terminal and the cathode terminal can be shortened, and therefore a capacitor with low ESL at high frequencies can be realized. In the capacitor according to the present invention, the terminals are led out in the same direction and overlap each other at least partially in the direction perpendicular to the terminal plane, and therefore the both terminals are coupled relatively strongly at high frequencies. For that reason, ESL of this capacitor can be reduced more.
The present invention also provides a capacitor built-in board including the above-described capacitor.
This capacitor built-in board includes a first wiring circuit layer, a second wiring circuit layer, a resin layer and the above-described capacitor. The resin layer and the capacitor are arranged between the first wiring circuit layer and the second wiring circuit layer, the anode terminal of the capacitor is connected electrically with a first wiring conductor formed on a main surface of one selected from the first wiring circuit layer and the second wiring circuit layer, and the cathode terminal of the capacitor is connected electrically with a second wiring conductor formed on a main surface of one selected from the first wiring circuit layer and the second wiring circuit layer. With this configuration, a small-sized and high-performance high frequency capacitor built-in board can be realized.
The capacitor built-in board of the present invention may further include a third, a fourth wiring circuit layers and so on and a second, a third resin layers and so on that are interposed between these wiring circuit layers to be configured as a multilayer wiring board, e.g., as a multilayer wiring board in which a wiring circuit layer and a resin layer are laminated alternately.